Red phosphorus castable smoke producing composition

ABSTRACT

A castable pyrotechnic white smoke composition which comprises red phosphorous, an alkali metal nitrate, magnesium and a suitable castable polymeric binder.

Artz

ited States Patent [451 Mar. 21, 1972 RED PHOSPHORUS CASTABLE SMOKEPRODUCING COMPOSITION Glen D. Artz, Canoga Park, Calif.

North American Rockwell Corporation Oct. 6, 1969 Inventor:

Assignee:

Filed:

Appl. No.:

U.S. Cl ..149/19,149/30,149/38, 149/43, 149/44, 149/61, 149/62, 149/88Int. Cl; 3.1.? ..L';'. .,C06d 3/00 Field of Search 149/29, 30, 19, 38,43, 44, 149/61, 62, 88

References Cited UNITED STATES PATENTS 6/1922 Nichols 149/30 PrimaryExaminer-Carl D. Quarforth Assistant ExaminerE. A. Miller Attorney L.Lee Humphries and Thomas S. MacDonald [5 7] ABSTRACT A castablepyrotechnic white smoke composition which comprises red phosphorous, analkali metal nitrate, magnesium and a suitable castable polymericbinder.

l 1 Claims, No Drawings RED PHOSPHORUS CASTABL'E SMOKE PRODUCINGCOMPOSITION Smoke markers or grenades are very useful in both militaryand commercial applications. In military applications, smoke markers canbe used to identify target sites. Additionally, in both commercial andmilitary applications such smoke markers are used for rescue operationsto identify parties being retrieved. In order for a smoke marker to bereadily handleable, it should be capable of being placed in a closed canor container which in some instances can actually be a grenade. If thesmoke composition is so disposed in an enclosed container, it must besusceptible to generating smoke without the presence of oxygen or air.In other words, the composition should be self-sustaining. Further,smoke composition should be preferably capable of slow dissipation ofthe smoke over a given period of time, to allow for identification ofthe area in which the smoke is originating.

Prior to the herein invention, white phosphorous had often been utilizedas the main smoke generating ingredient in various compositions.However, whitephosphorous has a drawback in that it is spontaneouslycombustible in air, which makes it extremely dangerous to handle.Further, white phosphorous rapidly dissipates smoke and does not allowfor a gradual release thereof.

Little effort had been directed in the past to the use of redphosphorous smoke compositions. When red phosphorous was used it was inthe form of pressed powder and was not cast as a grain. This is anexpensive, time consuming and sometimes dangerous process. Further,pressed powders do not have the structural integrity of cast grains. Theprevious pressed red phosphorous compositions additionally need air inorder to burn and were not self-sustaining, and thus could not be usedin closed containers where air could not reach the material.

Thus an object of this invention is to provide a self-sustainingcastable white smoke composition.

Another object of this invention is to provide a self-sustainingcastable smoke composition containing red phosphorous.

Still another object of this invention is to provide a castable -whitesmoke composition which has a long and controlled burn time.

The above and other objects of this invention are accomplished by anovel castable white smoke composition of this invention based on redphosphorous which will burn in the absence of atmospheric oxygen. Thecomposition of the invention contains red phosphorous as a primary fuelingredient to generate the smoke. The composition additionally containsan alkaline metal nitrate as an oxidizer. Additionally, the compositioncontains a metallic fuel, such as magnesium, in a relatively smallamount. Finally, the composition is held together by a castable binderwhich additionally serves as a fuel. Virtually any polymeric binderwhich is suitable for solid propellant utilization can be used. It ispreferred that the binder have a relatively high oxygen content and thatit cure to a rubbery state. A typical example of such a binder is theclass of polysulphide rubbers. Additional other materials in smallamounts, such as cross-linking agents, plasticizers, fillers andthe'like can be present in the composition. The ingredients aretypically mixed together in a suitable mixer, poured into the containersor hardware for the smoke composition, and cured at suitable curingconditions of temperature and pressure. By varying the composition andincluding the use of reactive plasticizers, one can subtly control theburning rate of the smoke compositions ofthis invention.

It is believed that the invention will be better understood from thefollowing detailed description and examples.

The main component of the smoke composition of this invention is redphosphorous. As indicated, prior to this invention, red phosphorous wasvery seldom used in smoke compositions. For example, in an early patent,U.S. Pat. No. 528,5]5, red phosphorous was combined with nitrate andpressed in one embodiment to form a composition which would produce abright flash of light. However, it was not disclosed as a smokegenerating composition. Where red phosphorous has been previously usedin an attempt to form a smoke generating composition, it additionallywas in a pressed form, not cast, and required the presence of air toburn. White phosphorous, on the other hand, has been used mostly in thepast in smoke compositions. However, it is spontaneously combustible inair, as indicated, and does not provide a slow controlled dissipation ofsmoke.

The red phosphorous used in this invention can vary from 31 to 47 weightpercent of the smoke composition. Red phosphorous is normally in a fineparticle form. It is not readily obtainable in various size particles.Because of this, one cannot readily achieve a high solid loading in acast composition, and thus the upper limit of 47 weight percent of thematerial is determined by a solids loading capability for castcompositions.

An alkali metal nitrate is used in the composition of this invention asan oxidizer. Typical nitrates include sodium and potassium nitrates. Oneof the primary problems in forming a suitable composition is an unwantedreaction between the oxidizer and the phosphorous. Thus, highly reactivematerials, such as the chlorates and perchlorates, are not suitable forthe compositions of this invention. The nitrate is used in a solidparticulate form in amounts varying from 18 to 32 weight percent of thesmoke composition.

In order to generate a hot enough flame to sustain burning of thephosphorous, magnesium is added to the composition of the invention.Magnesium reacts with the nitrate present to generate the heat requiredfor continued combustion of the phosphorous without snuffing out.Further, the reaction of the magnesium with the nitrate helps to providereliable ignition of the smoke composition. It has been found that from4 to 5 weight percent magnesium in the smoke composition serves toaccomplish the aforegoing purposes.

In order to form a suitable castable smoke composition, a polymericbinder is used. Virtually any binder which has been found suitable forsolid propellant compositions can be used herein. However, it is notdesirable to have the smoke composition too rigid or brittle, since itis subject often to shock loads particularly when it is used as agrenade. In fact it is preferred that the polymer cure to a rubberystate.

Additionally, it has been found desirable to have a high oxygencontaining binder because the quantity of solid oxidizer required can bereduced if the binder can supply some of the oxygen required foroxidation of the phosphorous and other fuels present in the composition.As a result, preferred binders include the polysulfide rubbers,polysulfide-epoxy mixtures such as Thiokol LP-3/Dow Epoxy DER 321 andDER 736 and polyesters produced from the reaction of dibasic acids withdihydric alcohols. A typical polyester binder is hydroxy-terminatedpolyester resin R-l 8 as supplied by Mobay Chemical Co. formed fromadipic acid and diethylene glycol. Additionally, hydroxy and carboxyterminated butadienes are further contemplated. In fact, any of thepolymeric binders set forth can be used herein. Together with thepolymer material, there is generally utilized a suitable plasticizer andcross-linking agent.

Various suitable plasticizers are contemplated, which are conventionaland well known in the art depending upon the binder selected. Typicalplasticizers include, for example, triacetin,bis-dinitropropylacrylate-formal (BDNPA-F), andtrimethylolethanetrinitrate (TMETN). Various other plasticizers, ofcourse, are contemplated and can be used.

In addition to the plasticizers, the binder composition will have acertain amount of cross-linking material added thereto. Preferredcross-linking material is PAPI which is polymethylenepolyphenylisocyanate. Additional cross-linking agents could include, butare not limited to for example, trimethylolpropane, hexanetriol, castoroil, toluene diisocyanate, diphenyl-methane diisocyanate and MAP0 whichis tris [l-(2-methyl)-aziridinyl] phosphine oxide.

Generally, the binder and plasticizer, if present, will constitute from25 to 35 weight percent of the smoke composition. The weight ratio ofplasticizer to hinder can vary from :1 to 1.521. The cross-linking agentwill vary from to 20 weight percent of the active binder material,depending upon the materials used and the state of cure desired in theend product.

Further, it has been found that FEAA, which is ferric acetylacetonate,can be added to the composition of this invention to provide acceleratedcure. Generally from 0.001 to 0.01 weight percent of EEAA is added forthis purpose. Other accelerators can be used to hasten the cure time.Selection of fuel accelerators will depend on the composition chosen.For example, when TMETN is a plasticizer then trimethylolpropane TMP, isa most suitable accelerator together with FEAA.

It should be pointed out that the aforegoing composition ranges setforth provide a smoke that is underoxidized. In other words, from astoichiometric standpoint there is not enough oxidizer present tofurnish oxygen for the full combustion of the fuel components. This isvery important to the herein invention in that it has been found that infully oxidized or over oxidized compositions the smoke will burn toovigorously in an uncontrollable manner. However, the composition doesprovide a castable smoke which does burn in the absence of atmosphericoxygen. Prior to the herein invention a castable red phosphorous smokecomposition which will burn in the absence of air was not believed to beknown.

The formulation of the smoke is simple and straightforward. Generallythe magnesium, phosphorous, plasticizer, and binder are first added to amixer and mixed at a suitable temperature for a period of time toachieve homogeneity. The nitrate is then added and additional mixingunder vacuum is accomplished at the mixed temperature. A vacuum isutilized at this stage to remove any air entrapped in the composition sothat more dense castings can be made. Finally, after the nitrate hasbeen mixed into the composition the cross-linking agent and otheradditives such as the FEAA are added and the final mix continued untilall the materials have been thoroughly dispersed. It is preferred tovacuum cast the mixture into prepared hardware used, such as cans orgrenades or any other suitable containers for the smoke composition.Casting conditions will of course vary depending upon the binder andcross-linking agents utilized. As indicated, the cure should provide arubbery final composition as compared to a brittle or rigid one.

In order to start or initially ignite the smoke composition an igniteris required. The smoke composition of this invention can be ignited byvirtually any ignition technique utilized for solid propellant ignition.These include a boron/potassium nitrate pellet, electric squibs,electric detonators and explosive materials such as Detacord, Primacord,and Pyroeore. Additionally a first fire mix or igniter mix can be coatedonto a surface. A typical ignition composition is comprised of silicon,lead oxide and cuprous oxide which would be mixed with nitrocellulose ina suitable solvent to form a lacquer that is spread onto the surface tobe ignited. It is believed that the invention will be further understoodfrom the following detailed examples.

EXAMPLE I A 5,000-gram batch of a smoke composition of this inventionwas prepared having the following composition expressed in weightpercent. In this and the following examples the percent accelerator isadded above the entire composition of the A standard l-gallonBaker-Perkins vertical mixer commonly used for solid propellant mixingwas used to mix the ingredients of this invention. The polyester binder,triacetin, magnesium, and phosphorous were all initially added to themixer and mixed for 15 minutes at F. The mixing was then stopped and thesodium nitrate was then added and mixing continued for an additional 10minutes under vacuum at F. After completion of this time period the PAP!and FEAA were then finally added and the mixing was continued for anadditional 10 minutes at 160 F. under vacuum. At this point, the mixingof the smoke composition was complete and ready for casting. Thecomposition was vacuum cast into polyethylene tubes which were 2% incheslong and had a diameter of three-fourths of an inch. The filled tubeswere placed in an oven and cured at 160 F. for 16 hours to a rubberystate.

These filled tubes were ignited by an electric squib and the burn timesevaluated by visual observation and a stopwatch. Standard solidpropellant strand burning rate equipment (Atlantic Research Corp.),which provides automatic recording of burn times, has also been utilizedfor burn rate evaluation although open air tests are preferable forobvious reasons.

The aforegoing composition was determined to have a buming rate of 0.70inch per minute. This composition was additionally found to have anautoignition temperature in excess of 500 F. and was insensitive toimpact with a 5 pound weight from a height of at least 50 inches. Thecomposition burned with a bright yellow flame and produced voluminousquantities of white smoke.

EXAMPLE II A slow burning formulation was tested as compared to thatdescribed in Example 1. The composition of the smoke in this examplecomprised:

Compound Wt.

Red Phosphorous 46.90 Sodium Nitrate 18.30 Magnesium 4.60 Mobay R-18Polyester Binder 14.00 Triacetin 15.80 PAP] 1.40 FEAA (added) 0.02

EXAMPLE III A fast burning formulation in accord with this invention wasformulated for this example using the procedures of Example I and thesame polyethylene tubes for casting the grain. The composition used inthis example comprised:

Compound Wt. 7:

Red Phosphorous 31.30 Sodium Nitrate 31.30 Magnesium 4.50 Mobay R-l8Polyester Binder 1 1.60 PAPl 0.90 TMETN 20.30 TMP (added) 0.10 FEAA(added) 0.02

Because of the presence of the TMETN instead of the triacetin, togetherwith the TMP, burning rates varying from 1.57 to 2.16 inches/minute wereobtained from samples tested. This indicates that the burning rate ofthis composition was from two to three times as great as the compositionset forth in Example I. Once again, this composition burned with abright yellow flame producing large quantities of white smoke.

lclaim:

1. A castable smoke producing composition comprising from 31 to 47weight percent red phosphorous, from 18 to 32 weight percent alkalimetal nitrate, from 4 to 5 weight percent magnesium and from to 35weight percent of a castable polymeric binder.

2. The composition of claim 1 in which said alkali metal nitrate ispotassium nitrate or sodium nitrate.

31 The composition of claim 1 in which the castable polymeric binder isa castable polysulphide, polysulphideepoxy mixture, polyester orpolybutadiene.

4. The composition of claim 3 in which the polybutadiene is a hydroxy orcarboxy terminated polybutadiene.

5. The composition of claim 3 in which the polyester is prepared by thereaction of a dibasic acid with a dihydric a1- cohol.

6. The composition of claim 5 in which the dibasic acid is adipic acidand the dihydric alcohol is diethylene glycol.

7. The composition of claim 1 in which the castable polymeric binderincludes a suitable plasticizer and cross-linking agent.

8. The composition of claim 7 in which the cross-linking agent ispresent in an amount of from 10 to 20 weight percent based on a totalcastable polymeric binder content.

9. The composition of claim 7 in which the plasticizer istrimethylolethanetrinitrate, triacetin, orbisdinitropropylacrylate-formal.

10. The composition otlciaim 7 in whichthe cross-linking agent ispolymethylene polyphenylisocyanate.

l 1. The composition of claim 7 in which the composition includes from0.001 to 0.01 weight percent of ferric acetylacetonate catalyst.

2. The composition of claim 1 in which said alkali metal nitrate ispotassium nitrate or sodium nitrate.
 3. The composition of claim 1 inwhich the castable polymeric binder is a castable polysulphide,polysulphide-epoxy mixture, polyester or polybutadiene.
 4. Thecomposition of claim 3 in which the polybutadiene is a hydroxy orcarboxy terminated polybutadiene.
 5. The composition of claim 3 in whichthe polyester is prepared by the reaction of a dibasic acid with adihydric alcohol.
 6. The composition of claim 5 in which the dibasicacid is adipic acid and the dihydric alcohol is diethylene glycol. 7.The composition of claim 1 in which the castable polymeric binderincludes a suitable plasticizer and cross-linking agent.
 8. Thecomposition of claim 7 in which the cross-linking agent is present in anamount of from 10 to 20 weight percent based on a total castablepolymeric binder content.
 9. The composition of claim 7 in which theplasticizer is trimethylolethanetrinitrate, triacetin, orbis-dinitropropylacrylate-formal.
 10. The composition of claim 7 inwhich the cross-linking agent is polymethylene polyphenylisocyanate. 11.The composition of claim 7 in which the composition includes from 0.001to 0.01 weight percent of ferric acetylacetonate catalyst.